release-24.3: sqlstats: clarify latency percentile limitations

[dhartunian]

Previously, there were some band-aids in place to limit the confusion around latency percentile estimates for SQL stats. These limitations cannot be obscured and result in confusion from customers.

This PR takes the opposite approach:

• Removal of code that would artificially clamp down reported quantiles to hide inconsistencies with max.
• Addition of explanatory text to DB Console to clarify the limitations of these numbers.

Resolves #139253

Release note: None

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Additional note: This PR is going directly onto 24.3 because these features are removed in master.

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Release justification: low-risk high impact change

[blathers-crl]

Thanks for opening a backport.

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[cockroach-teamcity]

This change is